Polycarbonates have been known for a number of years. U.S. Pat. No. 3,301,824 (1967) describes the preparation of carbonate homopolymers and random copolymers with cyclic lactones. While the patent generally discloses that the polymers have utility in moldings, coatings, fibers and plasticizers, there is no appreciation whatsoever of biodegradable fibers composed in whole or in part of polycarbonate "biopolymers".
In addition, there is no appreciation for the usefulness and importance of substituted poly(aliphatic carbonates) as fiber-forming polymeric compositions. By contrast, it is caprolactone, the dominant co-monomer, which offers the necessary crystalline character needed for fiber formation.
U.S. Pat. Nos. 4,243,775 (1981) and 4,429,080 (1984) disclose the use of polycarbonate-containing polymers in certain medical applications, especially sutures and other medical fasteners. However, this disclosure is clearly limited only to "ABA" and "AB" type block copolymers where only the "B" block contains poly(trimethylene carbonate) or a random copolymer of glycolide with trimethylene carbonate. The A block is necessarily limited to polyglycolide, which confers the crystalline character in the polymer necessary for fiber formation; and thus, the major portion of the polymers is the glycolide.
Accordingly, the art has failed to fully appreciate the potential biological or medical uses of biopolymers based on carbonates, especially with respect to their biodegradable or bioresorbable properties, as well as the wide range of mechanical properties achievable with these materials.
Bioresorbable polymers have been used in the fabrication of devices for implantation in living tissue for several decades. Medical application of such polymers include absorbable sutures, haemostatic aids and, recently, intraosseous implants and slow-release drug delivery systems, to name but a few.
Use of such polymers has been extended to tissue regeneration devices such as nerve channels, vascular grafts, sperm duct channels, fallopian tube ducts or channels and the like. To be effective, these devices must be made from materials that meet a wide range of biological, physical, and chemical prerequisites. The material must be bioresorbable at least in part, nontoxic, noncarcinogenic, nonantigenic, and must demonstrate favorable mechanical properties such as flexibility, suturability in some cases, and amenability to custom fabrication. The biopolymers of the present invention have all of those attributes.